Add a WatchedLongSparseArray

Bug: 179648149

Add a WatchedLongSparseArray class and use it in
PackageManagerService.  This includes a unit test for the new class.

Test: atest
 * FrameworksServicesTests:AppsFilterTest
 * FrameworksServicesTests:PackageInstallerSessionTest
 * FrameworksServicesTests:PackageManagerServiceTest
 * FrameworksServicesTests:PackageManagerSettingsTests
 * FrameworksServicesTests:ScanTests
 * FrameworksServicesTests:UserSystemPackageInstallerTest
 * PackageManagerServiceBootTest
 * UserLifecycleTests#startUser
 * UserLifecycleTests#stopUser
 * UserLifecycleTests#switchUser
 * android.appsecurity.cts.EphemeralTest
 * android.appsecurity.cts.InstantAppUserTest
 * FrameworksServicesTests:WatcherTest

Change-Id: If0dfde203db7a85ded3cf409981d58518a13990b